The present invention relates generally to improvements in needle valves, and more particularly, but not by way of limitation, to the construction of seals for valves of this type.
Needle valves generally comprise a class of valves in which a circular valve member, or needle, is mounted in a valve body for axial movement into an obstructing relation with a flow passage formed through the valve body. Usually, such movement is accomplished by forming threads on the valve member to mate with corresponding threads formed in a portion of the valve body so that the axial movement of the valve member can be effected by turning the valve member. In a particular type of needle valve, the valve member comprises a frusto-conical member, which alternatively obstructs the flow passage or is displaced therefrom to permit flow through the valve, and a threaded valve stem which extends axially from the larger end of the frusto-conical member. In this species of needle valve, the flow passage extends transversely to the axis of the frusto-conical member and it is known to include a liner, or seal, which receives the frusto-conical member and is mounted in a valve chamber formed within the valve body to intersect the flow passage.
Needle valves of the particularly described type have the potential for offering a variety of advantages in the control of fluid flow. In particular, because of the relative simplicity of construction of valves of this type, a potential exists for providing a valve capable of operation under a variety of conditions, including high pressure applications, with little or no maintenance and at a relatively low cost. However, prior to the present invention such potential has not been fully realized because of problems that exist with respect to the seals in prior art valves of this type. For the valve to operate, the seal must have apertures formed therethrough to align with openings of the flow passage into the valve chamber and the seal must be held in place within the valve chamber to maintain such alignment. In addition, the seal must also tightly engage portions of the valve chamber wall which are pierced by the flow passage openings and the frustoconical member, when the valve is closed, to prevent leakage through the valve. While it is possible to construct needle valves to meet these criteria, such construction has, in the past, generally been accompanied with increased machining costs, difficulty in assembly of the valve, or both. Alternatively, where cost and ease of assembly are important factors in the manufacture of a valve, compromises have been made in the sealing effectiveness of the valve or in the applications to which a valve might be put; for example, low cost might be achieved by limiting the valve to low pressure applications.